Background: The aim of this in vitro study was the evaluation of the mechanical\r\nproperties the screws for rapid maxillary expansion (RME).\r\nMethods: Three commercially available screws for RME were tested: Leone A2620;\r\nDentaurum Hyrax; Forestadent Palatal Split Screw. All expansion screws were 10 mm\r\nin size. For the evaluation of mechanical properties, the screws for RME were\r\nadjusted using the same maxillary dental model. An Instron 3365 testing machine\r\nwith a load cell of 5 kN recorded the forces released by the screws at different\r\namounts of activation (1, 5, 10, 15 and 20 quarters of a turn). Each type of screw was\r\ntested 10 times. Comparisons between the forces released by the different types of\r\nscrews at different amounts of activation were carried out by means of analysis of\r\nKruskal-Wallis test with post-hoc test di Tukey (P < 0.05).\r\nResults: The results of this study showed that all 3 expansion devices were able to\r\ndevelop forces that could produce a separation of the palatine processes. The Hyrax\r\nand A2620 expanders developed force values over 20 kg and the Palatal Split screws\r\nabout 16 kg. Both the A2620 and Hyrax expanders showed significantly greater\r\namounts of forces at all the different amounts of activations with respect to the\r\nPalatal Split screw.\r\nConclusions: All tested devices showed the capability of developing expansion\r\nforces (16-20 kg) adequate for RME. The A2620 and Hyrax expanders showed a\r\ngreater level of rigidity than the Palatal Split screw.
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